William Blake and the Imagination in Ideas of Good and Evil by William Butler Yeats.

“He was a symbolist who had to invent his symbols” [via]

Consider also:

  1. “This letter may have been the expression of a moment’s enthusiasm, but was more probably rooted in one of those intuitions of coming technical power which every creator feels, and learns to rely upon; for all his greatest work was done, and the principles of his art were formulated, after this date. Except a word here and there, his writings hitherto had not dealt with the principles of art except remotely and by implication; but now he wrote much upon them, and not in obscure symbolic verse, but in emphatic prose, and explicit if not very poetical rhyme.”
  2. “when man’s desire to rest from spiritual labour, and his thirst to fill his art with mere sensation and memory, seem upon the point of triumph, some miracle transforms them to a new inspiration”
  3. “A symbol is indeed the only possible expression of some invisible essence, a transparent lamp about a spiritual flame; while allegory is one of many possible representations of an embodied thing, or familiar principle, and belongs to fancy and not to imagination: the one is a revelation, the other an amusement.”
  4. “Again and again one finds some passing allusion to the cave of man’s mind, or to the caves of his youth, or to the cave of mysteries we enter at death, for to Shelley as to Porphyry it is more than an image of life in the world.”
  5. “This philosophy kept him more simply a poet than any poet of his time, for it made him content to express every beautiful feeling that came into his head without troubling about its utility or chaining it to any utility.”